Optimizing remote direct memory access (rdma) with cache aligned operations

ABSTRACT

A system for optimizing remote direct memory accesses (RDMA) is provided. The system includes a first computing device and a second computing device disposed in signal communication with the first computing device. The first and second computing devices are respectively configured to exchange RDMA credentials during a setup of a communication link between the first and second computing devices. The exchanged RDMA credentials include cache line size information of the first computing device by which a cache aligned RDMA write operation is executable on a cache of the first computing device in accordance with the cache line size information by the second computing device.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.14/867,395 which was filed on Sep. 28, 2015. The entire disclosures ofU.S. application Ser. No. 14/867,395 are incorporated herein byreference.

BACKGROUND

The present invention relates to remote direct memory access (RDMA) and,more specifically, optimization of RDMA with cache aligned operations.

In computing, RDMA relates to direct memory access operations from thereal local memory of one computer into the real local memory of anothercomputer without the need to involve certain components of eithercomputer's operating system. This permits high-throughput, low-latencynetworking, which is especially useful in massively parallel computerclusters. Applications of RDMA support zero-copy networking by enablinglocal network adapters to transfer data directly to or from applicationmemory, thereby eliminating a need to copy data between applicationmemory and data buffers in the operating system. Such transfers requireno work to be done by central processing units (CPUs), caches or contextswitches, and allow for transfers to continue in parallel with othersystem operations. That is, when an application performs an RDMA read orwrite operation, the relevant application data is delivered directly tothe peer's physical memory via the network to reduce latency and enablefast message or data transfer.

RDMA technology broadly supports write, read and autonomous updates ofcomputer system memory and there are many communication protocols thatallow application programming interfaces (APIs) to enable exploitationof RDMA based technology over various communications media, such asInfiniband, Ethernet and long distant networks (WAN). However, when RDMAbased technology is to be exploited, there are numerous performanceconsiderations relating to remote memory access processes that should beaddressed.

One such consideration is that RDMA operations (e.g., RDMA-writeaccesses) should if possible be handled on a processor cache line basisand applies to both the local and the remote hosts. That is, when datais written to a remote peer's memory, it may be

beneficial to perform write operations on a cache line boundary and on afull cache line basis (vs. non-aligned or partial write operations whenpossible) since the penalty for not aligning the write operations canresult in moderate to severe latency with respect to the local hostcomputer's DMA operations to the local host memory sub-system. Indeed,an unaligned large write operation can result in hundreds of unalignedDMA write operations (depending on total transfer and packet size) withthe eventual amount of latency varying based on the remote peer'splatform hardware and memory sub-system (i.e., the remote peer's adaptercard, PCIe bus, memory sub-system architecture, etc.).

The injected latency in DMA operations can cause local congestion thatresults in overall network latency and even packet loss that in turnresults in retransmission, pause frames and other congestion controlactions that lead to poor overall performance.

SUMMARY

According to an embodiment of the present invention, a system foroptimizing remote direct memory accesses (RDMA) is provided. The systemincludes a first computing device and a second computing device disposedin signal communication with the first computing device. The first andsecond computing devices are respectively configured to exchange RDMAcredentials during a setup of a communication link between the first andsecond computing devices. The exchanged RDMA credentials include cacheline size information of the first computing device by which a cachealigned RDMA write operation is executable on a cache of the firstcomputing device in accordance with the cache line size information bythe second computing device.

According to another embodiment of the present invention, a computerprogram product for optimizing remote direct access memory accesses(RDMA) is provided. The computer program product includes a computerreadable storage medium having program instructions stored thereon. Theprogram instructions are executable by respective processing circuits offirst and second computing devices to cause the respective processingcircuits to exchange RDMA credentials during a setup of a communicationlink between the first and second computing devices. The exchanged RDMAcredentials include cache line size information of the first computingdevice by which a cache aligned RDMA write operation is executable on acache of the first computing device in accordance with the cache linesize information by the second computing device.

According to yet another embodiment of the present invention, acomputer-implemented method for optimizing remote direct memory accesses(RDMA) is provided. The method includes exchanging RDMA credentialsbetween first and second computing devices during a setup of acommunication link between the first and second computing devices,including, within the exchanged RDMA credentials, cache line sizeinformation of the first computing device, saving the exchanged RDMAcredentials, including the cache line size information of the firstcomputing device, in a persisting state and executing, in accordancewith the cache line size information, a cache aligned RDMA writeoperation by the second computing device on a cache of the firstcomputing device.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter which is regarded as the invention is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The forgoing and other features, and advantages ofthe invention are apparent from the following detailed description takenin conjunction with the accompanying drawings in which:

FIG. 1 is a schematic diagram of a computing system in accordance withembodiments;

FIG. 2 is a schematic diagram of a portion of a memory unit of a firstcomputing device of the computing system of FIG. 1;

FIG. 3 is a schematic diagram of a portion of a memory unit of a secondcomputing device of the computing system of FIG. 1;

FIG. 4 is a schematic diagram of a computer program product of thecomputing system of FIG. 1 in accordance with embodiments;

FIG. 5 is a schematic illustration of an exchange of RDMA credentials ofthe computer program product of FIG. 4 when deployed in the computingsystem of FIG. 1;

FIG. 6 is a schematic illustration of data superimposed over physicalmemory that is shown as being sectioned into individual cache lineswhere the data does not begin or end on a cache line boundary(unaligned);

FIG. 7 is a flow diagram illustrating a deployment process for thecomputer program product of FIG. 4 in accordance with embodiments; and

FIG. 8 is a flow diagram illustrating a computer-implemented method foroptimizing RDMA operations in accordance with embodiments.

DETAILED DESCRIPTION

There are several problems that prevent a host transport protocol fromreliably handling RDMA operations (e.g., RDMA-write accesses) on aprocessor cache line basis and thereby optimizing RDMA-read/writeoperations. These include, but are not limited to the unpredictablenature of upper layer application (user) data patterns, size, boundaryalignment and other characteristics owing to application datarequirements that can vary significantly and cannot be restricted andthe possibility that the transmitting host is unaware of the cache linesize of the remote peer host. Thus and, as will be described below, acomputer program product and a computer-implemented method of optimizingRDMA with cache aligned operations is provided to allow for acommunication or exchange of platform cache line size informationbetween peers.

That is, while previous implementations of RDMA based technology canassume cache line size in what is at best a functional but not optimalmanner and transport protocols can impose restrictions on target memoryalignment rules and usage patterns which limits application datapatterns, creates additional memory exchange signaling overhead orimposes additional API and memory architecture restrictions, theoptimized RDMA described herein does not rely on merely functionalassumptions of cache line size and imposes no restrictions on targetmemory alignment rules and usage patterns.

With reference to FIG. 1, a computing system 10 is provided and may beconfigured for example as an enterprise computing system or as apersonal computing system. In either case, the computing system 10includes at least first computing device 11 and second computing device12, which are configured to be networked together for communicationpurposes and thus are disposable in signal communication with eachother. It will be understood, of course, that additional computingdevices could be provided in the computing system 10 but these are notdescribed herein for purposes of clarity and brevity.

Each of the first and second computing devices 11 and 12 includes amongother features a processing circuit 20, a memory unit 25, a display 30,user input devices 40 and a networking unit 50 as well as a computerprogram product 100 for optimizing RDMA. The processing circuit 20 maybe provided as a micro-processor, a central processing unit (CPU) or anyother suitable processing device. The display 30 may be provided as amonitor and is configured to display data and information as well as agraphical user interface to an administrator or user. The user inputdevices 40 may be provided as a mouse and a keyboard combination and areconfigured to allow the administrator or user to input commands to theprocessing circuit 20. The networking unit 50 may be provided as anEthernet or other suitable networking device by which the first andsecond computing devices 11 and 12 are communicative with each other.

With reference to FIGS. 2 and 3, respective portions of the memory units25 of the first and second computing devices 11 and 12 will now bedescribed. As shown in FIG. 2, the portion of the memory unit 25 of thefirst computing device 11 may include various types of random-access andread-only memory and may be provided with a first cache 110. This firstcache 110 may be configured with multiple cache lines 111 that each havemultiple address locations defined at sequential points along theirrespective lengths. The respective sizes of the multiple cache lines 111may be varied or unique with respect to cache line sizes of other cachesand may be provided, for example, as 64 byte cache lines, 128 byte cachelines or 256 byte cache lines. Similarly, as shown in FIG. 3, theportion of the memory unit 25 of the second computing device 12 mayinclude various types of random-access and read-only memory and may beprovided with a second cache 120. This second cache 120 may beconfigured with multiple cache lines 121 that each have multiple addresslocations defined at sequential points along their respective lengths.The respective sizes of the multiple cache lines 121 may be varied orunique with respect to cache line sizes of other caches and may beprovided, for example, as 64 byte cache lines, 128 byte cache lines or256 byte cache lines.

It is to be understood that the first cache 110 and the second cache 120are both separate from the respective main memories of the first andsecond computing devices 11 and 12 and both may have unique cache linesizes in accordance with various factors including, but not limited to,processor architecture.

In an exemplary case in which the second computing device 12 executes anon-optimized RDMA write operation on the first cache 110 of the firstcomputing device 11, the non-optimized RDMA write operation effectivelybecomes a DMA read operation by the second computing device 12 followedby DMA write operation at the first cache 110. Thus, when the secondcomputing device 12 initiates the non-optimized RDMA write operation onthe first cache 110, the first RDMA write operation begins at a firstbyte offset for the length of data to be transmitted and the next writeoperation starts directly after the last (previous) byte is written orat a byte offset following the last byte of the previous RDMA writeoperation. In other words, if the first RDMA write operation on thefirst cache 110 was for a length of 4500 (×1194) bytes, the (first) ornext RDMA write operation will start at a remote buffer area +4 (+4 toaccount for the 4 byte control header of the remote buffer area) andwill end at 4504 (×1198) and a subsequent RDMA write operation willstart at the next available byte at byte offset +4505 (×1199) and so on.

For each of the RDMA write operations, a full line store refers to thoseincidents where RDMA write operations start at beginnings of cache linesand have lengths that correspond to the sizes of those cache lines.Conversely, partial store operations occur when byte offsets are notcache aligned or where RDMA write operations have less data than a fullcache line. Such partial stores can be non-optimal and may lead tolatency related to direction of data flows, workload patterns, PCIeconfiguration Node/PBU, the incidence (frequency) of concurrent partialstores, etc.

However, if the second computing device 12 aligns RDMA-write operationsto begin on cache line boundaries, the numbers of partial storeoperations at the first cache 110 could be significantly reduced ascompared to cases in which an initial operation is not aligned and theassociated penalty occurs for every subsequent packet. Indeed, a 32knon-optimized RDMA-write operation executed by the second computingdevice 12 may generate 32 packets (e.g., with a 1k maximum transmissionunit (MTU) or a similar value) at some offset into the first cache 110where each packet will normally cause 2 partial store operations(non-aligned) along with 2 line store operations (aligned stores) whenthe target system has a 256 byte cache line size for a total of 64partial stores along with approximately 64 line stores in anon-optimized case. Conversely, an optimized RDMA write operation wouldbegin on a cache line 111 rounding up to the next cache aligned offset.After all full cache lines are written, the remaining non-aligned datais written resulting in minimal partial stores. This approach reducesthe partial stores to 2 (1 at the beginning and 1 at the end of theentire optimized RDMA write operation) yielding in a 64 to 2 partialstore reduction in the exemplary case. This approach represents apotential for significant savings with the larger the payload (i.e., theoptimized RDMA write operation), the larger the opportunity for savings.

Thus, with reference to FIGS. 4-6, the computer program product 100includes a computer readable storage medium 1001 having programinstructions 1002 stored thereon. The program instructions 1002 areexecutable by the respective processing circuits 20 of each of the firstand second computing devices 11 and 12 to cause the respectiveprocessing circuits 20 to exchange RDMA credentials 1003 during a setupof a communication link 1004 (se FIG. 1) between the first and secondcomputing devices 11 and 12. In accordance with embodiments, theexchanged RDMA credentials 1003 may include, for example, cache linesize information of the first cache 110 of the first computing device11. Using this cache line size information and in accordance therewith,a cache aligned RDMA write operation is executable on the first cache110 by the second computing device 12.

As shown in FIG. 5, the program instructions 1002 are executable by theprocessing circuit 20 of the second computing device 12 to configure thesecond computing device 12 to issue a link request 10031 to the firstcomputing device 11 along the communication link 1004. Meanwhile, theprogram instructions 1002 are executable by the processing circuit 20 ofthe first computing device 11 to configure the first computing device 11to issue a link response 10032 to the second computing device 12 inresponse to the link request 10031. This link response 10032 may includeone of a first indication 10033 and a second indication 10034.

The first indication 10033 may be provided as a “0000” bit and indicatesto the second computing device 12 that an align RDMA write option (ARW)is unsupported by the first computing device 11. The second indication10034 indicates to the second computing device 12 that the ARW issupported by the first computing device 11 for predefined cache sizes.That is, if the cache lines 111 of the first cache 110 have 64 bytecache line sizes, the second indication 10034 may be in the form of a“0001” bit, if the cache lines 111 of the first cache 110 have 128 bytecache line sizes, the second indication 10034 may be in the form of a“0010” bit and if the cache lines 111 of the first cache 110 have 256byte cache line sizes, the second indication 10034 may be in the form ofa “0011” bit.

It is to be understood that the link request 10031 and the link response10032 may both be sent by both of the first and second computing devices11 and 12 and need not be one-way communications.

Where the first indication 10033 is received by the second computingdevice 12 or where no link response at all is issued, RDMA alignmentneed not commence. However, where the second indication 10034 isreceived, the second computing device 12 proceeds with preparation of anoptimized RDMA write operation by adjusting the original RDMA writeoperation to correspond to the size requirements of the cache lines 111of the first cache 110 of the first computing device 11. Suchadjustment, as shown in FIG. 6, may initially include recognizing, bythe second computing device 12, from the save cache line value that wasoriginally received in the second indication 10034 of the sizes of thecache lines 111 and determining, by the second computing device 12 of anend point of previously stored data. Thus, for a case where the cachelines 111 have 256 byte cache line sizes, the second computing device 12will determine at an initiation of the optimized RDMA write operationthat the end point of previously stored data on the first cache 110 islocated at first data end point (offset) 600 defined at about 2/3 of thelength of the second cache line 111 ₂.

At a next stage of the optimized RDMA operation, the second computingdevice will effectively split the optimized RDMA write operation intotwo operations by calculating the remaining length of the second cacheline 111 ₂ from a rounding up from the first data end point 600 to thenext cache line boundary 601. The second computing device 12 will thenskip an equivalent length of the unaligned data and transmit theremaining portion of the RDMA write operation data 602 with a singlealigned RMDA write operation (e.g., the third cache line 111 ₃ to thenth cache line 111 _(n). This will cause the corresponding adapter tobuild and send the corresponding packets (based on the networktransmission size specifications such as MTU). Once the first portion ofthe RDMA write operation data 602 is sent and stored in cache line 111_(n+1), a data pad 603 that can be overwritten later is added to thecache line 111 _(n−1) in case the cache line 111 _(n+1) is onlypartially filled. At this point, the second computing device 12 sends alast packet of a second portion of the unaligned RDMA write operationdata 604, which includes the data that was originally skipped. As such,even where n is a large number, only 2 partial stores are generated bythe optimized RDMA write operation.

In accordance with embodiments, once the last byte of the second portionof the RDMA write operation data 604 is complete, metadata may now betransmitted or appended with information that will describe all of thedata that was transferred (e.g., as a data availability notification inthe form of a separate signal packet).

While it is understood that the program instructions 1002 may bedeployed by manual loading thereof directly into a client, server and/orproxy computer by way of a loadable storage medium, such as a CD, DVD,etc., being manually inserted into each of the first and secondcomputing devices 11 and 12, the program instructions 1002 may also beautomatically or semi-automatically deployed into the computing system10 by way of a central server 15 or a group of central servers 15 (seeFIG. 1). In such cases, the program instructions 1002 may bedownloadable into client computers that will then execute the programinstructions 1002.

In accordance with alternative embodiments, the program instructions1002 may be sent directly to a client system via e-mail with the programinstructions 1002 then being detached to or loaded into a directory.Another alternative would be that the program instructions 1002 be sentdirectly to a directory on a client computer hard drive. When there areproxy servers, however, loading processes will select proxy servercodes, determine on which computers to place the proxy servers' codes,transmit the proxy server codes and then install the proxy server codeson proxy computers. The program instructions 1002 will then betransmitted to the proxy server and subsequently stored thereon.

In accordance with embodiments and, with reference to FIG. 7, adeployment process of the computer program product described above isprovided. The process begins at block 700 and at block 101 with adetermination of whether the program instructions 1002 will reside on aserver or servers when executed. If so, then the servers that willcontain the executables are identified at block 209. The programinstructions 1002 for the server or servers are then transferreddirectly to the servers' storage via FTP or some other protocol or bycopying though the use of a shared file system at block 210 such thatthe program instructions 1002 are installed on the servers at block 211.

Next, a determination is made on whether the program instructions 1002are to be deployed by having users access the program instructions 1002on a server or servers at block 102. If so, the server addresses thatwill store the program instructions 1002 are identified at block 103 anda determination is made if a proxy server is to be built at block 200 tostore the program instructions 1002. A proxy server is a server thatsits between a client application, such as a Web browser, and a realserver and operates by intercepting all requests to the real server tosee if it can fulfill the requests itself. If not, the proxy serverforwards the request to the real server. The two primary benefits of aproxy server are to improve performance and to filter requests.

If a proxy server is required, then the proxy server is installed atblock 201 and the program instructions 1002 are sent to the (one ormore) servers via a protocol, such as FTP, or by being copied directlyfrom the source files to the server files via file sharing at block 202.Another embodiment involves sending a transaction to the (one or more)servers that contained the process software, and have the server processthe transaction and then receive and copy the process software to theserver's file system. Once the process software is stored at theservers, the users may then access the program instructions 1002 on theservers and copy to the same to their respective client computer filesystems at block 203. Alternatively, the servers may automatically copythe program instructions 1002 to each client and then run aninstallation program for the program instructions 1002 at each clientcomputer whereby the user executes the program that installs the programinstructions 1002 on his client computer at block 212 and then exits theprocess at block 108.

At block 104, a determination is made as to whether the programinstructions 1002 are to be deployed by sending the program instructions1002 to users via e-mail. If a result of the determination isaffirmative, the set of users where the program instructions 1002 willbe deployed are identified together with the addresses of the userclient computers at block 105 and the program instructions 1002 are sentvia e-mail to each of the users' client computers. The users thenreceive the e-mail at block 205 and then detach the program instructions1002 from the e-mail to a directory on their client computers at block206. The user executes the program that installs the programinstructions 1002 on his client computer at block 212 and then exits theprocess at block 108.

Lastly, a determination is made on whether the program instructions 1002will be sent directly to user directories on their client computers atblock 106. If so, the user directories are identified at block 107 andthe process software is transferred directly to the user's clientcomputer directories at block 207. This can be done in several ways suchas, but not limited to, sharing the file system directories and thencopying from the sender's file system to the recipient user's filesystem or, alternatively, using a transfer protocol such as FileTransfer Protocol (FTP). The users access the directories on theirclient file systems in preparation for installing the programinstructions 1002 at block 208, execute the program that installs theprogram instructions 1002 at block 212 and then exit the process atblock 108.

With reference to FIG. 8, a method for optimizing RDMA is provided. Themethod includes exchanging RDMA credentials 1003 between the first andsecond computing devices 11 and 12 during a setup of the communicationlink 1004 between the first and second computing devices 11 and 12 atblock 801, including, within the exchanged RDMA credentials 1003, cacheline size information of the first computing device 11 at block 802,saving the exchanged RDMA credentials 1003 including the cache line sizeinformation, in a persisting state in the second computing device 12 atblock 803 and executing, in accordance with the cache line sizeinformation, a cache aligned RDMA write operation by the secondcomputing device 12 on a cache 110 of the first computing device 11 atblock 804.

The descriptions of the various embodiments of the present inventionhave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiments, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdisclosed herein.

The present invention may be a system, a method, and/or a computerprogram product at any possible technical detail level of integration.The computer program product may include a computer readable storagemedium (or media) having computer readable program instructions thereonfor causing a processor to carry out aspects of the present invention.

The computer readable storage medium can be a tangible device that canretain and store instructions for use by an instruction executiondevice. The computer readable storage medium may be, for example, but isnot limited to, an electronic storage device, a magnetic storage device,an optical storage device, an electromagnetic storage device, asemiconductor storage device, or any suitable combination of theforegoing. A non-exhaustive list of more specific examples of thecomputer readable storage medium includes the following: a portablecomputer diskette, a hard disk, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), a static random access memory (SRAM), a portablecompact disc read-only memory (CD-ROM), a digital versatile disk (DVD),a memory stick, a floppy disk, a mechanically encoded device such aspunch-cards or raised structures in a groove having instructionsrecorded thereon, and any suitable combination of the foregoing. Acomputer readable storage medium, as used herein, is not to be construedas being transitory signals per se, such as radio waves or other freelypropagating electromagnetic waves, electromagnetic waves propagatingthrough a waveguide or other transmission media (e.g., light pulsespassing through a fiber-optic cable), or electrical signals transmittedthrough a wire.

Computer readable program instructions described herein can bedownloaded to respective computing/processing devices from a computerreadable storage medium or to an external computer or external storagedevice via a network, for example, the Internet, a local area network, awide area network and/or a wireless network. The network may comprisecopper transmission cables, optical transmission fibers, wirelesstransmission, routers, firewalls, switches, gateway computers and/oredge servers. A network adapter card or network interface in eachcomputing/processing device receives computer readable programinstructions from the network and forwards the computer readable programinstructions for storage in a computer readable storage medium withinthe respective computing/processing device.

Computer readable program instructions for carrying out operations ofthe present invention may be assembler instructions,instruction-set-architecture (ISA) instructions, machine instructions,machine dependent instructions, microcode, firmware instructions,state-setting data, configuration data for integrated circuitry, oreither source code or object code written in any combination of one ormore programming languages, including an object oriented programminglanguage such as Smalltalk, C++, or the like, and procedural programminglanguages, such as the “C” programming language or similar programminglanguages. The computer readable program instructions may executeentirely on the user's computer, partly on the user's computer, as astand-alone software package, partly on the user's computer and partlyon a remote computer or entirely on the remote computer or server. Inthe latter scenario, the remote computer may be connected to the user'scomputer through any type of network, including a local area network(LAN) or a wide area network (WAN), or the connection may be made to anexternal computer (for example, through the Internet using an InternetService Provider). In some embodiments, electronic circuitry including,for example, programmable logic circuitry, field-programmable gatearrays (FPGA), or programmable logic arrays (PLA) may execute thecomputer readable program instructions by utilizing state information ofthe computer readable program instructions to personalize the electroniccircuitry, in order to perform aspects of the present invention.

Aspects of the present invention are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems), and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer readable program instructions.

These computer readable program instructions may be provided to aprocessor of a general purpose computer, special purpose computer, orother programmable data processing apparatus to produce a machine, suchthat the instructions, which execute via the processor of the computeror other programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks. These computer readable program instructionsmay also be stored in a computer readable storage medium that can directa computer, a programmable data processing apparatus, and/or otherdevices to function in a particular manner, such that the computerreadable storage medium having instructions stored therein comprises anarticle of manufacture including instructions which implement aspects ofthe function/act specified in the flowchart and/or block diagram blockor blocks.

The computer readable program instructions may also be loaded onto acomputer, other programmable data processing apparatus, or other deviceto cause a series of operational steps to be performed on the computer,other programmable apparatus or other device to produce a computerimplemented process, such that the instructions which execute on thecomputer, other programmable apparatus, or other device implement thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof instructions, which comprises one or more executable instructions forimplementing the specified logical function(s). In some alternativeimplementations, the functions noted in the blocks may occur out of theorder noted in the Figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts or carry out combinations of special purpose hardwareand computer instructions.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of onemore other features, integers, steps, operations, element components,and/or groups thereof.

The descriptions of the various embodiments of the present inventionhave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiments, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdisclosed herein.

What is claimed is:
 1. A system for optimizing remote direct memoryaccesses (RDMA), the system comprising: a first computing device; and asecond computing device, RDMA credentials being exchangeable between thefirst and second computing devices during a first and second computingdevice communication link setup, and the exchanged RDMA credentialscomprising cache line size information of the first computing device bywhich a write operation is executable by the second computing device. 2.The system according to claim 1, wherein: the second computing device isconfigured to issue a link request to the first computing device, andthe first computing device is configured to issue a link response to thesecond computing device in response to the link request, the linkresponse comprising a first indication that an align write option isunsupported by the first computing device or a second indication thatthe align write option is supported by the first computing device for apredefined cache size.
 3. The system according to claim 1, wherein thewrite operation is adjustable.
 4. The system according to claim 1,wherein the write operation comprises an addition of a trailing pad towrite operation data.
 5. The system according to claim 1, wherein thewrite operation comprises a definition of a start address.
 6. The systemaccording to claim 1, wherein the write operation comprises atransmission of a first portion of write operation data and a secondportion of the write operation data with metadata.
 7. The systemaccording to claim 1, wherein the write operation comprises respectivetransmissions of first and second portions of write operation data infirst and second write operations.
 8. The system according to claim 1,wherein the second computing device generates a data availabilitynotification for the first computing device upon completion of the writeoperation.
 9. A computer program product for optimizing remote directaccess memory accesses (RDMA), the computer program product comprising:a computer readable storage medium having stored thereon: programinstructions executable by respective processing circuits of first andsecond computing devices to cause the respective processing circuits toexchange RDMA credentials during a first and second computing devicecommunication link setep, the exchanged RDMA credentials comprisingcache line size information of the first computing device by which awrite operation is executable by the second computing device.
 10. Thecomputer program product according to claim 9, wherein: the programinstructions are executable by the processing circuit of the secondcomputing device to configure the second computing device to issue alink request to the first computing device, and the program instructionsare executable by the processing circuit of the first computing deviceto configure the first computing device to issue a link response to thesecond computing device in response to the link request, the linkresponse comprising one of a first indication that an align write optionis unsupported by the first computing device or a second indication thatthe align write option is supported by the first computing device for apredefined cache size.
 11. The computer program product according toclaim 9, wherein the write operation comprises an adjustment.
 12. Thecomputer program product according to claim 9, wherein the writeoperation comprises an addition of a trailing pad.
 13. The computerprogram product according to claim 9, wherein the write operationcomprises a definition of a start address.
 14. The computer programproduct according to claim 9, wherein the write operation comprises atransmission of a first portion of write operation data and a secondportion of the write operation data with metadata.
 15. The computerprogram product according to claim 9, wherein the write operationcomprises respective transmissions of first and second portions of writeoperation data in first and second write operations.
 16. The computerprogram product according to claim 9, wherein the program instructionsare executable by the processing circuit of the second computing deviceto configure the second computing device to generate a data availabilitynotification for the first computing device.